This invention relates to a wheel rim of an assembling system installed on a rimbase for a pneumatic tire and a side flange on the movable side of a lockring. The lockring has a cutting portion on the periphery of the lockring having breaks between discontinuous portions of the lockring; the rimbase interconnected through the lockring to a bead seat band.
Heretofore, such kind of wheel rim has generally a structure consisting of a rimbase 1, a side flange 2, a bead seat band 3, a lockring 4 and a O-ring 5 as shown in FIG. 1. However, in the conventional example described above, the lockring 4 is adapted to form a leg portion 4a engaged in a lockring groove 6 and a surface 4b positioned across a gutter edge 7 of the rimbase 1, and a sectional shape having an inclined surface 4c of about 45.degree. at another side as shown in FIG. 2. When compressed air is filled in the tire, a side pressure acts on the bead seat band 3 toward the outside through the side flange 2 on the movable side and the side of the lockring groove 6 of the rimbase 1 is pressed toward the outside through the lower inclined portion of the bead seat band 3 and the inclined surface 4c of the lockring 4. By this, the component force of side pressure of said inclined surface 4c supplies a force in a radial direction to a gutter edge 7 by said side pressure, whereby the tire is engaged.
In other words, the side pressure F caused by the pressure of tire acts on the side wall of the lockring groove 6 in the rim base 1 and a component force in the radial direction of the side pressure of the inclined surface 4C in the lockring 4 acts on the gutter edge surface 7 as a pressure P. Futher, said gutter edge surface 7 is subjected to a variable load of a vertical load which acts on the tire.
Accordingly, an edge portion a of the bottom of the lockring groove 6 in the rimbase 1 is subjected to a great stress by F and P+W and the like, thereby there exists a problem such as the occurrence of a crack b due to a fatigue breakdown.